Glutamine plays a key role in metabolism as the donor of an NH2 group in the biosynthesis of purines, pyrimidines, histidine, o- and p- aminobenzoic acids, amino sugars, nicotinamide coenzymes, asparagine, and glutamic acid. In addition, glutamine appears to be important under certain conditions in the nutrition and maintenance of nitrogen balance in microorganisms and mammalian cells in culture. This project is concerned with several features of the functions and metabolic significance of enzymes directly involved in transformations of glutamine ("amidotransferases" and "glutaminases"), including: (a) the mechanisms of action of certain of these enzymes, especially as revealed with the use of site-specific analog inhibitors, (b) comparative biochemistry of the enzymes: an examination of whether structural resemblances occur in the active site regions and more peripherally in the relevant protein molecules which would indicate evolutionary derivation from a common prototype, (c) studies on the interrelationship of glutamine, glutamic acid, and ammonia pools in bacteria in different metabolic states as regulated by glutaminases and amidotransferases, and (d) an examination of the system for asparagine synthesis with particular emphasis on attempts to develop specific inhibitors of the enzyme involved. The latter study has as goals not only clarification of the mechanism of the reaction, but the more practical one of testing agents which may prove to be of therapeutic value in controlling the growth of certain tumors which seem to be abnormally dependent upon supply of asparagine.